kleidiai: Add SME vs SME2 distinction in kernel dispatch (#25478)

The current integration treats SME as a single capability (CPU_FEATURE_SME)
with no distinction between SME(v1) and SME2. The kernels dispatched under
CPU_FEATURE_SME use SME2-specific instructions, making dispatch incorrect
on SME(v1)-only hardware.

We introduce build-time and runtime distinction between SME and SME2, and
wire SME(v1) and SME2 kernels based on actual hardware support.

ggml/src/ggml-cpu/ggml-cpu.c

@@ -3792,6 +3792,14 @@ int ggml_cpu_has_sme(void) {
 #endif
 }
 
+int ggml_cpu_has_sme2(void) {
+#if defined(__ARM_ARCH) && defined(__ARM_FEATURE_SME2)
+    return 1;
+#else
+    return 0;
+#endif
+}
+
 void ggml_cpu_init(void) {
     // needed to initialize ggml_time
     {